It is often a goal, in areas such as electronics, organic and inorganic chemical catalysis, and electrochemistry, to rapidly and economically apply to surfaces chemical activating agents. Particularly in the fabrication of microelectronic devices, optics, integrated circuits, and the like, it is desirable to deposit patterned metal pathways on a surface in an economically and environmentally sound manner.
A variety of processes are available for forming electrically-conductive pathways on substrates. As an example of a photolithographic process, a metal film can be laminated to a non-conductive substrate, a photoresist applied to the metal laminate layer and exposed to light through a mask in a pattern corresponding to the desired pathway, the non-irradiated portion of the photoresist removed, newly-exposed portions of the metal laminate layer etched, and the photoresist removed to expose a metal pathway corresponding to the pattern of irradiation applied to the photoresist. Other techniques for applying metal pathways to surfaces include the well-known "silk screening" technique, in which a paste containing finely-divided metal particles in a carrier is applied, for example, via a screen including a pattern, to a substrate in a pattern corresponding to the screen pattern. The paste is fired and a conductive metal pathway having a pattern corresponding to the screen pattern results.
Electroless deposition is a process widely used for the application of metals such as copper, gold, silver, nickel, rhodium, cobalt, and others to substrates. Electroless deposition occurs by an autocatalytic redox process, in which the cation of the metal to be deposited is reduced by a soluble reductant at the surface of a catalyst used to initiate the deposition, and subsequently at the surface of the metal feature being formed. This redox process generally takes place only on catalytic surfaces, that is, surfaces that inherently are catalytic to the redox process or surfaces that first are activated with a catalyst. Several methods are known for patterning a catalyst on a non-catalytic substrate. That is, selectively activating a substrate in a pattern corresponding to an ultimate pattern of metal deposition. U.S. Pat. No. 4,472,428 (Sirinyan et al.) describes a process for the production of metalized semiconductors using a process involving application of catalyst across a surface, applying a polymeric material, through a mask having a pattern, to the surface, plating a metal on the surface, and dissolving the template to produce a patterned metal layer.
U.S. Pat. No. 4,322,457 (Baron et al.) describes patterned metal deposition that involves applying a surfactant to a substrate in a pattern (via, for example, conventional printing techniques) applying a precursor of a catalytic agent to the surface (e.g. Pd.sup.2+), allowing the precursor to be "buried" such that the surfactant covers the precursor in the originally-applied pattern, rinsing the surface, exposing the surface to an agent to convert the precursor to a catalyst (e.g. Pd), and plating a metal at the surface in a pattern complementary to the original pattern.
U.S. Pat. No. 4,192,762 (Madsen) describes patterned metal deposition that involves coating a surface with a reducible salt of a non-noble metal and a radiation-sensitive reducing agent, irradiating the surface in a pattern to reduce the metal salt to a reduced catalyst in a pattern corresponding to the pattern of irradiation, and plating a metal at the pattern exposing the catalyst.
U.S. Pat. Nos. 3,873,359, 3,873,360, and 3,900,614 (Lando) describe patterned metal deposition involving, according to a first embodiment, coating a substrate with a colloidal wetting solution capable of converting a catalyst precursor, such as palladium chloride, to a catalyst, using a stamp having a raised pattern to transfer to the surface the catalyst precursor so that the precursor reacts at the surface to form the catalyst in the pattern, and plating metal at the surface at the patterned catalytic region. According to a second embodiment, the method involves coating the surface with a catalyst precursor such as palladium chloride, using a stamp to transfer to the surface a reducing agent that converts the precursor to the catalyst in a pattern corresponding to the stamp pattern thereby reacting the precursor, in the patterned region, to produce the catalyst, and plating the metal at the surface in the pattern. According to a third embodiment, the method involves transferring to the surface, in a pattern, a reducing agent capable of reacting with a catalyst precursor to form a catalyst, exposing the surface to a catalyst precursor whereby a reaction occurs forming the catalyst in the pattern, and plating metal on the surface in the pattern.
Dressick et al., Chem. Mater., 5, 148-150 (1993) describe chemisorption of ligand-bearing organosilanes onto a surface, deep UV irradiation through a patterned mask to selectively remove the organosilane in the pattern, application to the surface of a Pd(II) solution to immobilize the Pd(II) species at the regions at which the ligand remains, and electroless deposition of a metal at those regions.
The above-described methods typically are relatively time-consuming and expensive in that they involve several steps including, for example, prior to plating a metal in a pattern on a surface, carrying out a chemical reaction at the surface to convert a precursor to a reactant needed in the plating reaction, and/or involve relatively expensive equipment such as photolithographic apparatus, and/or involve the consumption of chemical reactants and generation of corresponding chemical waste to an undesirable extent.
Accordingly, a general purpose of the present invention is to provide a method of conveniently, quickly, inexpensively, and reproducibly applying to a surface a chemical activating agent in a manner that renders unnecessary at least some of the above-described procedural steps, reactants, waste products, time, and expense. Another purpose of the invention is to produce a variety of metal patterns on surfaces without these complications. Another purpose of the invention is to provide a convenient method for producing a metal pattern on a nonplanar surface. Another purpose of the invention is to provide metal pathways on substrates that are conveniently and inexpensively manufactured.